1. Field of the Invention
The present invention relates to a cathode-ray tube (CRT) used for constituting a display apparatus which forms a large or gigantic picture to be seen by a great number of people in grounds or the like.
2. Description of the Prior Art
It is known that a large number of, say, approximately 30,000 CRTs 1 are arranged in the matrix form to constitute a display apparatus as illustrated in FIG. 1 and the intensity of illumination of each CRT constituting one picture element is so controlled as to display a gigantic picture collectively.
A current of several milliamperes is let flow through a CRT constituting a conventional display apparatus. Accordingly, the video drive voltage of several tens volts is required for driving the intensity of illumination at the fluorescent screen. Since an extremely large number of CRTs are installed, a large number of drive circuits are also required. As a result, a large total power is required, resulting in poor economy.
It is also known that a conventional color display apparatus is composed of a number of, say approximately 30,000 colored but monochrome tubes 11 arranged in a matrix form as illustrated in FIG. 2 and the intensity of illumination of each colored but monochrome tube is so controlled that the apparatus as a whole may display a gigantic picture. In such a color display apparatus, colored but monochrome tubes 11 respectively radiating blue (B), green (G) and red (R) monochromatic lights are alternately arranged as illustrated in FIG. 2 to display a gigantic color picture.
In such a conventional color display apparatus, however, one CRT radiates a monochromatic light and three CRTs (G, B and R) constitute one picture element. Accordingly, three times as many color tubes as picture elements are necessitated. Thus, the total number of color CRTs is large, resulting in a high cost. In addition, such a conventional color display apparatus has a drawback that its size can not be reduced because of difficulty in reducing the size of a picture element.